Reference is made to commonly-assigned copending U.S. Patent Application Serial No. 10/228,877, filed concurrently herewith, entitled xe2x80x9cLong Life Charging Apparatus,xe2x80x9d by Michael Zona et al., the disclosure of which is incorporated herein.
The present invention concerns a charging member for charging a material to be charged such as a light sensitive material for use in electrophotography and electrostatic recording processes in image forming apparatus such as electrophotographic copying machines and printers. More specifically, it relates to a charging member to be pressed on the surface of a material to be charged such as a light sensitive material and a dielectric material for uniformly charging the surface of the material to be charged, and a charging device.
In electrophotographic apparatus, uniform charge is applied to the surface of a material to be charged such as a light sensitive material or a dielectric material. A method of conducting the charging function by using corona generation by applying a high voltage to metal wires has been adopted as a charging treatment means. However, the corona charging method involves a drawback in that corona-induced products such as ozone and nitrogen oxides (NOx) formed upon charging and denature the surface of the light sensitive material to deteriorate the light sensitive material or cause image blurring, and that the contamination of the wires gives an undesired effect on the image quality, leading to image deletions.
In addition to the non-contact method described above, there is a contact method of charging by bringing a charging member into contact, or near contact, with a material to be charged. The contact, or near contact, type charging method has an advantage that a voltage to be applied to the charging member is generally low and the amount of ozone formed is extremely small. However, it has three major drawbacks. The first is the electrical stability of the selected material set over the life of the said contact-charging device. Depending on the type of conduction method selected, the conduction medium can drift within the material causing the electrical properties of the charging member to change over time, thereby causing non-uniform charging or stressing of the high voltage power supply that applies high voltage to the charging member. The second difficulty is the achievement of uniform charge in the length-wise direction of the charging member. The uniformity of the charge applied by the charging member is largely attributed to the dimensional uniformity of the contact interface between the said charging member and the member to be charged. The last major challenge in contact type charging is to overcome non-uniform charging caused by toner and toner additive contamination that occurs on the surface of the charging member.
In view of the above, an aspect of the present invention is to prevent deterioration of the charging performance of a charging member caused by contamination of the surface layer of the charging member, to maintain stable and satisfactory uniform charging property, and image quality for a long period of time.
A further aspect of the present invention is to prevent non-uniform charging of the member to be charged by providing a means of maintaining uniform width of the contact interface between the charging member and the member to be charged.
There is provided an apparatus for charging a substrate, comprising: an elongated charging member having a crowned surface; an elongated pressure member having said pressure member being supported for pressure engagement with said charging member to form a nip therebetween adapted to receive the substrate.
There is also provided a printing machine having apparatus for charging a substrate, comprising: an elongated charging member having a crowned surface; an elongated pressure member having, said pressure member being supported for pressure engagement with said charging member to form a nip therebetween adapted to receive the substrate.